The invention relates to an optical slip ring for communication of data with a rotor, the slip ring comprising at least one light emitter mounted on the rotor or on an adjacent fixed support, at least one light receiver on the other of the rotor or fixed support, a drive means for delivering data signals to each emitter, and a receiver means for receiving signals from each light receiver and providing an output signal. The term "high speed" rotor is intended to cover rotors having a speed in excess of 5000 rmp with continuous rotation.
Methods of transmitting data across a rotary interface involve use of direct mechanical contact or optical technologies. Mechanical contact/rubbing methods, such as brush, wire, sliding and mercury wetted contacts, are subject to a number of disadvantages. Contact jitter, vibration and environmental noise all contribute to noise levels in the transmitted signal. Dirt accumulation and wear necessitate periodic maintenance and low speeds and lifetimes are also dictated by wear. Each circuit will contain differing values of contact resistance which will change over the individual contacts' lives. It is also difficult to obtain a relatively high density of channels compared to length on the axis of rotation.
Regarding optical slip rings, systems such as those described in U.S. Pat. Nos. 4,519,670 and 4,943,137 involve use of complex light control elements such as lenses and diffractive gratings. A system based on colour multiplexing is described in British Patent Specification NO. GB 2,109,189 in which signals are passed through optical fibres. WO 85/02270 and EP 45585 also describe systems based on use of optical fibres. It appears that such systems would have a limited range of application because of the limitations imposed by use of fibres rotation, alignment of joints, and their fragile nature generally.
U.S. Pat. Nos. 4,190,318 and 4,958,904 describe optical slip ring arrangements in which rather complex arrangements of emitters and receivers are used to ensure that there is effective signal transmission at all times. For example, FIG. 7 of U.S. Pat. No. 4,190,318 shows superimposition of signal intensity for a uniform signal level. A very large number of receivers are used in the arrangement described in U.S. Pat. No. 4,958,904.
U.S. Pat. No. 4,278,323 describes an optical slip ring for very low speed applications such as rotation of a tank turret. An optical fibre arrangement is used, which does not appear to be suitable for high speed applications.
There is therefore a need for an optical slip ring which is suitable for high speed applications to such as turbine rotors, in which there may be a very high data throughput. An example is capture of data from strain gauges on rotating turbine blades in which the data transfer should allow analysis of the blade resonant frequencies. The system must be capable of processing captured data in real time.